1. Field of the Invention
The present invention relates to a photographing apparatus having an automatic focusing system for generating a distance signal corresponding to the distance between the apparatus and an object to be photographed.
2. Description of the Prior Art
There have been proposed various types of automatic focusing systems for measuring the distance between a photographing apparatus and an object to be photographed and generating a distance signal which is to be used as a drive signal for driving a photographing lens, such as, e.g., described in U.S. Patent Application Ser. No. 121,690 as filed Feb. 15, 1980 (corresponding to Japanese Patent Application Laid-open No. 115,023/1980 laid open on Sept. 4, 1980).
The known automatic focusing systems may be roughly classified into a passive type and an active type. An automatic focusing system of the passive type receives light reflected from an object, processes a signal corresponding to the received light to obtain a distance to the object and then moves the photographing lens to an in-focus position. Another automatic focusing system of the same type moves the photographing lens in response to the shutter release operation while receiving the light transmitted through the photographing lens so that, on the basis of the processing of the changes in the light transmitted every moment through the lens, the movement of the photographing lens is stopped. An automatic focusing system of the active type emits light for the measurement of the distance from the photographing apparatus to the object, receives the light reflected by the object, and generates an automatic focusing signal. In automatic focusing systems of either type, an optical signal corresponding to the object distance is converted into an electric signal, and this electric signal is then processed whereby the photographing lens is moved accordingly to the in-focus position. For operating the automatic focusing system, there are known two focusing modes. According to one focusing mode, the operation for measuring the distance to an object is performed only once, after the power is turned on. According to the other focusing mode, focusing signals are generated in response to the changes in the object distance due to the movement of the object. In the automatic focusing system having the latter focusing mode, that is, the focusing mode wherein the focusing signals are generated in response to the changes in the object distance (to be referred to as "continuous focusing mode" hereinafter), distance signals may be generated and the photographing lens may be moved accordingly upon the movement of the object, even during the period from the start of the exposure control operation (for example, depression of the shutter releast button) . . . opening of the shutter in response to the operation of the exposure control mechanism . . . closing of the shutter . . . until the completion of the exposure of the photosensitive material. For this reason, it is not clear to an operator whether the photographing operation is effected under the in-focus state at the time immediately before the shutter release operation or under the conditions just upon completion of the shutter release operation, i.e., after the object has been moved. It is therefore not clear to the operator whether the subject has been photographed in a composition as intended.